System and method for producing an image with a screen using erase (off) and image (on) light sources

ABSTRACT

An image system includes a beam generator and a screen having a region with an adjustable brightness. The beam generator directs first and second electromagnetic beams onto the region. The first beam changes the brightness of the region according to a first polarity and the second beam changes the brightness of the region according to a second polarity. Such an imaging system can generate a video frame on a projection screen such that each pixel of the frame is “on” for the same or approximately the same amount of time as each of the other pixels. This technique prevents portions of the image from appearing visibly dimmer than other portions. It also allows the persistence of the screen regions to be relatively long, e.g., longer than the frame rate, and thus allows the screen to display/project relatively high-quality video frames.

TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates generally to imaging systems, and moreparticularly to an imaging system that scans a display/projection screenwith multiple energy beams. For example, the system can first scan aregion of the screen with an erase beam that sets the brightness of theregion to a predetermined erase level. Then, the system can scan theregion with an image beam that sets the brightness of the region to thebrightness level of the corresponding region of the image being scanned.

BACKGROUND OF THE INVENTION

[0002] A variety of image-display/image-projection devices andtechniques are available for visually displaying/projecting graphical orvideo images—often called video frames—to a viewer. Typically, agraphical image is an image that changes slowly or not at all. Forexample, a flight-instrument graphic is an image of cockpit instrumentsthat overlays a pilot's view. This graphic may be projected onto aviewing area such as the windshield or may be projected directly intothe pilot's eyes such that he/she sees the flight instruments regardlessof his/her viewing direction. There is typically little change in thisgraphic other than the movement of the instrument pointers or numbers.Conversely, video frames are a series of images that typically changefrequently to show movement of an object. For example, a television setdisplays video frames.

[0003] A cathode-ray-tube (CRT) display, such as used in a television ora computer monitor, is a common image-display/image-projection devicethat, unfortunately, has several limitations. For example, a CRT istypically bulky and consumes a significant amount of power, thus makingit undesirable for many portable or head-mounted applications.

[0004] Flat-panel displays, such as liquid-crystal displays (LCDs),organic LEDs, plasma displays, and field-emission displays (FEDs), aretypically less bulky and consume significantly less power than a CRThaving a comparable viewing area. But, flat panel displays often lacksufficient luminance and adequate color purity and/or resolution formany head-mounted applications.

[0005] A common problem with both CRTs and flat-panel displays is thatthe displayed/projected image may include visible artifacts that areintroduced into the image during the capturing, processing, ordisplaying of the image. Typically, an image-capture device such as avidicon tube or charge-coupled device (CCD) captures an image of anobject by converting light reflected by the object into electricalsignals. A display/projection system that includes one of theaforementioned display/projection devices receives these electricalsignals and processes them. The display/projection device converts theseprocessed electrical signals into an array of pixels, which a viewerperceives as an image of the object. Unfortunately, visible errors anddegradations, often called artifacts, may be introduced into the imageduring the conversion of the reflected light into electrical signals,during the processing of the electrical signals, or during theconverting of the electrical signals into pixels.

[0006] Recently, engineers have developed an image amplifier that candisplay an image or project the image onto a display screen. Typically,an image amplifier is less complex, less expensive, and can be madesmaller than a CRT or flat-panel display, and an image-amplifier displaysystem typically uses significantly less power than a CRT or flat-paneldisplay system. Furthermore, because it does not necessarily convertlight into electrical signals and back again, an image-amplifier systemtypically introduces fewer artifacts into an image.

[0007]FIG. 1 is a perspective view of a conventional image-amplifierdisplay system 20 that includes an image amplifier 22, an illuminator24, and an image generator 26. For example, the image amplifier 22 maybe a Light Smith, which was developed by Simac Company of Boise, Id.Although, as discussed above, the system 20 is often less complex,cheaper, and smaller than a CRT or flat-panel display system, it candisplay/project a relatively bright and high-quality image 28.

[0008] The image amplifier 22 of the system 20 includes transparentfront and back electrodes 30 and 32 and a display/projection screen 34having a display/projection surface 36 and a scan surface 38. Anelectric-field generator (not shown) is coupled to the electrodes 30 and32 and generates an electric field across the screen 34. This electricfield allows the image generator 26 to set the brightness levels—herethe reflectivity levels—of the regions of the display/projection surface36 such that the generator 26 can generate bright and dark pixels of animage. For example, the generator 26 can set the reflectivity of theregion 44 on the surface 36 to a relatively high level such that theregion 44 reflects a relatively high percentage of the incident lightfrom the illuminator 24. Therefore, in this example, the pixel of theimage 28 corresponding to the region 44 is a relatively bright pixel.

[0009] The illuminator 24 typically includes an incoherent light sourcesuch as an incandescent bulb (not shown), which illuminates thedisplay/projection surface 36 of the screen 34. The surface 36 reflectsthe light from the illuminator 24 according to the reflectivity of eachregion 44 to display the image 28—that is, project the image 28 directlyinto a viewer's (not shown) eye—or to project the image 28 onto adisplay screen 46 through an optical train 47, which is represented by alens.

[0010] The image generator 26 generates the image 28 on thedisplay/projection surface 36 of the screen 34 by erasing the surface 36with an electromagnetic erase burst 40 and then scanning an image beam42 across the scan surface 38.

[0011] More specifically, erasing the surface 36 of the screen 34entails simultaneously setting all the regions 44 on the surface 36 tothe same or approximately the same predetermined reflectivity level withthe erase burst 40. Typically, this predetermined reflectivity level isa low reflectivity level—which represents black—although it can be anyother desired reflectivity level. The erase burst 40 typically is anenergy burst having a first wavelength in the visible, ultraviolet, orinfrared range of the electromagnetic spectrum and is wide enough tosimultaneously strike the entire scan surface 38. Where the erase levelis black, the screen 34 is typically constructed such that exposing thescan surface 38 to this first wavelength reduces the reflectivity levelsof the regions 44. Because these reflectivity levels may be differentfrom one another before the erase cycle, the generator 26 generates theburst 40 long enough to reduce the reflectivity levels of all theregions 44 to the black level regardless of their pre-erase reflectivitylevels. Furthermore, because it typically “turns off” the reflectivitiesof the regions 44, the burst 40 is sometimes called an “off” burst.

[0012] Generating the image 28 on the screen 34 entails scanning theimage beam 42 across the scan surface 38 to set the reflectivity levelsof the regions 44 such that the reflectivity levels correspond to thebrightness levels of the respective pixels of the image 28. The beam 42typically is an energy beam having a second wavelength in the visible,ultraviolet, or infrared range of the electromagnetic spectrum and has adiameter that equals or approximately equals the diameter of a region44. Typically, one can set the diameter of the beam 42—and thus thediameter of each region 44—small enough so that the image amplifier 22provides a high-resolution, high-quality image 28. Where the erase levelis black, the screen 34 is typically constructed such that exposing thescan surface 38 to this second wavelength increases the reflectivitylevels of the regions 44. The image generator 26 sets the reflectivitylevel of a region 44 by modulating the time that the image beam 42strikes the region of the scan surface 38 corresponding to the region44, by modulating the intensity of the beam 42 as it strikes thecorresponding region of the surface 38, or by modulating both theintensity and time. The generator 26 can modulate the intensity of thebeam 42 by modulating the power to the beam source (not shown) or withan acoustic-optic modulating crystal (not shown) in the path of the beam42. Because the reflectivity level of a region 44 starts out at a knownlevel—black for example—the generator 26 can use a look-up table orother techniques to determine a striking time or striking intensity thatwill set the region 44 to the desired reflectivity level. Furthermore,because it effectively “turns on” the reflectivities of the regions 44,the beam 42 is sometimes called an “on” beam.

[0013] Still referring to FIG. 1, in operation for still images, theimage generator 26 generates the erase burst 40 to erase the surface 36of the screen 34, and then scans the image 28 onto the surface 36.Specifically, the generator 26 scans the image beam 42 across the scansurface 38 of the display screen 34 to generate the image 28 on thesurface 36. In one embodiment, the persistence of the surface 36 isrelatively long such that once the beam 42 scans the image 28, thescreen 34 “holds” the image. “Persistence,” as used in reference to FIG.1, is the amount of time that a region 44 of the surface 36 retains thereflectivity level set by the beam 42. Therefore, if the persistence isrelatively long, e.g., hours, then the generator 26 need not rescan theimage 28 or may rescan the image 28 at relatively long intervals. Thegenerator 26 may scan the beam 42 according to any number ofconventional scanning techniques such as those described in U.S. Pat.No. 6,140,979, entitled “Scanned Display With Pinch, Timing, AndDistortion Correction”, which is incorporated by reference.

[0014] In operation, for a series of video frames, the image generator26 generates the erase burst 40 before each frame, and then scans theimage beam 42 across the surface 38 to generate the frame on thedisplay/projection surface 36. The generator 26 then repeats thissequence—generating an erase burst 40 and then scanning the surface 38with the beam 42—for each frame.

[0015] Unfortunately, a problem with generating video frames on along-persistence screen 34 is uneven brightness control within frames.Specifically, if the entire region is erased, the first region 44scanned by the image beam 42 has the desired reflectivity level for alonger time than the subsequently scanned regions, and for asignificantly longer time than the last-scanned region. Therefore, thefirst-scanned regions 44 may appear brighter on average than thelast-scanned regions. For example, assume that the image generator 26generates the erase burst 40 every T seconds, scans a first region 44with the image beam 42 virtually immediately after generating the eraseburst 40, and generates the next erase burst 40 t seconds after scanningthe last region 44. Therefore, the first-scanned region 44 has its “on”reflectivity for approximately T seconds, while the last-scanned region44 has its “on” reflectivity for only t seconds. Consequently, becausethe first-scanned regions 44 tend to be “on” longer than thelast-scanned regions 44, the first-scanned regions tend on average toappear brighter to the eye than the last-scanned regions 44. Thus, thismay cause the image 28 to have an uneven brightness.

[0016] One approach to addressing uneven brightness is to shorten thepersistence of the screen 34. For instance, referring to the aboveexample, one can construct the screen 34 such that the regions 44 eachhave a persistence of approximately t seconds such that each region 44,regardless of when it is scanned by the image beam 42, has its “on”reflectivity for approximately the same time.

[0017] While this solution may reduce the appearance of unevenbrightness, it will often reduce the overall brightness of the image 28,or may otherwise degrade the image 28.

SUMMARY OF THE INVENTION

[0018] In one aspect of the invention, an image system includes a beamgenerator and a screen having a region with an adjustable brightness.The beam generator directs first and second electromagnetic beams ontothe region. The first beam changes the brightness of the regionaccording to a first polarity and the second beam changes the brightnessof the region according to a second polarity.

[0019] Such an imaging system can generate a video frame on adisplay/projection screen such that each pixel of the frame is “on” forthe same or approximately the same amount of time as each of the otherpixels. This technique prevents portions of the image from appearingdimmer on average than other portions. It also allows the persistence ofthe screen regions to be relatively long, e.g., longer than the framerate, and thus allows the screen to display/project relativelyhigh-quality video frames.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is an isometric view of a conventional image-amplifierdisplay system.

[0021]FIG. 2 is an isometric view of an image-amplifier display systemaccording to an embodiment of the invention.

[0022]FIG. 3 is an isometric view of a linked image system that includesat least one image-amplifier display system of FIG. 1 or 2 according toan embodiment of the invention.

[0023]FIG. 4A is a diagram of an image captor/generator and an imageamplifier of FIG. 3 according to an embodiment of the invention.

[0024]FIG. 4B is a diagram of an image captor/generator and an imageamplifier of FIG. 3 according to another embodiment of the invention.

[0025]FIG. 5 illustrates a unidirectionalsingle-erase-beam/single-image-beam scanning technique that the systemsof FIGS. 2 and 3 can use according to an embodiment of the invention.

[0026]FIG. 6 illustrates a unidirectionalmultiple-erase-beam/multiple-image-beam scanning technique that thesystems of FIGS. 2 and 3 can use according to an embodiment of theinvention.

[0027]FIG. 7 illustrates a unidirectionalwide-erase-beam/multiple-image-beam scanning technique that the systemsof FIGS. 2 and 3 can use according to an embodiment of the invention.

[0028]FIG. 8 illustrates a unidirectional,multiple-erase-beam/multiple-image-beam tiling technique that thesystems of FIGS. 2 and 3 can use according to an embodiment of theinvention.

[0029]FIG. 9 illustrates a unidirectional,multiple-erase-beam/multiple-image-beam tiling technique that thesystems of FIGS. 2 and 3 can use according to another embodiment of theinvention.

[0030]FIG. 10 illustrates a switched-feed,multiple-erase-beam/multiple-image-beam tiling technique that thesystems of FIGS. 2 and 3 can use according to an embodiment of theinvention.

[0031]FIG. 11 illustrates a bidirectional,multiple-erase-beam/multiple-image-beam scanning technique that thesystems of FIGS. 2 and 3 can use according to an embodiment of theinvention.

[0032]FIG. 12 illustrates a bidirectional,single-erase-beam/multiple-image-beam scanning technique that thesystems of FIGS. 2 and 3 can use according to an embodiment of theinvention.

[0033]FIG. 13 is a top view of a color-image projection system accordingto an embodiment of the invention.

[0034]FIG. 14 is a top view of a color-image projection system accordingto another embodiment of the invention.

DESCRIPTION OF THE INVENTION

[0035]FIG. 2 is an isometric view of an image-amplifierdisplay/projection system 48 according to an embodiment of theinvention. As discussed below, the system 48 is similar to the system 20of FIG. 1 except that it uses an erase beam 52 to erase the regions 44instead of using the erase burst 40. Because the systems 20 and 48 aresimilar, components common to the systems 20 and 48 are referenced bylike numerals.

[0036] The system 48 includes an image generator 53, which generates theimage beam 42 and the erase beam 52. In one embodiment, the erase beam52 has the same wavelength as the erase burst 40 of FIG. 1, and thussets the reflectivity level of each region 44 of the display/projectionsurface 36 to a predetermined erase level such as black. But instead ofsimultaneously erasing all of the regions 44 with an erase burst, thegenerator 53 scans the erase beam 52 across the scanning surface 38ahead of the image beam 42. Therefore, unlike the erase burst 40, theerase beam 52 erases one region 44 at a time. The intensity of the beam52 is typically high enough to erase a region 44 in the time that thebeam 52 strikes the region regardless of the pre-erase reflectivitylevel of the region. Because this striking time is proportional to thehorizontal scan rate, the intensity of the erase beam 52 is typicallyhigher for higher scan rates so that the overall energy striking theregion 44 achieves the desired erase level even at higher scan rates.Furthermore, a distance d separates the image beam 42 from the erasebeam 52 in the scanning direction. Typically, d is wide enough toprevent the beams 42 and 52 from interfering with one another on thedisplay/projection screen 34. In addition, the separation betweenadjacent scan lines is sufficient such that the erase beam 52 does noterase any part of a previously written line. Alternatively, the erasebeam may lead the image beam 42 by one or more scan lines as discussedbelow in conjunction with FIG. 12.

[0037] In operation, the image generator 53 scans both the image beam 42and the erase beam 52 across the scan surface 38 of the screen 34 suchthat the erase beam 52 leads the image beam 42. The generator 53 mayscan the beams 42 and 52 in a digital fashion by deactivating the beamsin between the regions 44. Alternatively, the generator 53 may scan thebeams 42 and 52 in an analog fashion by keeping the beams activated inbetween the regions 44.

[0038] Consequently, the erase beam 52 erases a region 44, and, shortlythereafter, the image beam 42 sets the reflectivity of the region 44 tothe desired level. Therefore, for video frames, assuming that thepersistence of the screen 34 is longer than the frame rate, all of theregions 44 are “on” for approximately the same amount of time. This isunlike the system 20 of FIG. 1, where the last scanned regions 44 are“on” for a significantly shorter time than the first scanned regions.For example, assume that the frame rate, which is the time betweensuccessive scans of a region 44 by the image beam 42, is T seconds, andthe persistence of each region 44 is greater than T. Because the erasebeam 52 leads the image beam 42 by only a relatively small distance deach region 44 is erased approximately T seconds after being turned “on”by the image beam 42. Therefore, the system 48 can achieve morebrightness uniformity for a long persistence than system 20 can as thatdescribed above with reference to FIG. 1.

[0039] Although the image generator 53 is described above assimultaneously generating and scanning the image and erase beams 42 and52 spaced apart by a distance d, in another embodiment the generator 53scans a single beam (not shown) that toggles between the image-beamwavelength and the erase-beam wavelength. That is, the generator 53directs this single beam onto a particular region 44. For the firstperiod of the time that the beam strikes the region 44, the beam has theerase-beam wavelength, and for the second period of time that the beamstrikes the region 44, the beam has the image-beam wavelength. Thegenerator 53 then scans the single beam onto the next region 44.

[0040] Furthermore, techniques for scanning the beams 42 and 52 acrossthe scan surface 38 are discussed below in conjunction with FIGS. 5-12.

[0041]FIG. 3 is a perspective view of an optical-linked imaging system54, which includes a pair of image-display/image-capture systems 55 aand 55 b according to an embodiment of the invention. Because thedescribed embodiment of the system 54 is entirely optical—it does notconvert optical signals to electronic signals and back again—it mayeliminate some of the disadvantages of conventional non-optical imagingsystems. Prior optical-linked imaging systems are described in commonlyowned U.S. patent app. Ser. No. 09/129,739, entitled “Linked ScannerImaging System And Method”, which is incorporated by reference.

[0042] The image display/projection capabilities of the systems 55 a and55 b are similar to those of the system 48 of FIG. 2, but each of thesystems 55 a and 55 b can also capture an image, a series of images, ormay capture light generally from a location remote from the amplifiers22 a and 22 b, respectively. The system 55 a receives an image 56 fromthe system 55 b via a fiber-optic cable 58 and scans the image 56 ontoan image amplifier 22 a, which displays the image 56 or projects theimage 56 onto a display screen 46 a through an optical train 47 a. Thesystem 55 a also captures light, such as that corresponding to an image59 of an object 60—the object 60 may be an object like a tree, or aphoto or other likeness of the tree—and transmits the image 59 to thesystem 55 b via the cable 58. Likewise, the system 55 b receives theimage 59 from the system 55 a via the cable 58 and scans the image 59onto an image amplifier 22 b, which displays the image 59 or projectsthe image 59 onto a display screen 46 b through an optical train 47 b.The system 55 b also captures the image 56 of an object 61 and transmitsthe image 56 to the system 55 a via the cable 58.

[0043] The system 55 a includes an image generator/captor 62 a inaddition to the image amplifier 22 a, an illuminator 24 a, and thedisplay screen 46 a, which are similar to the amplifier 22, theilluminator 24, and the display screen 46 of FIG. 2. Thegenerator/captor 62 a scans an image beam 42 a and an erase beam 52 aacross the scan surface 38 a of the screen 34 a to generate the image 56on the display/project surface 36 a in a manner similar to thatdescribed above in conjunction with FIG. 2. The generator/captor 62 aalso captures the image 59 by scanning rays of light reflected from theobject 60 into the cable 58 as a continuous beam of light, i.e., anoptical signal, as discussed below in conjunction with FIGS. 4A and 4B.That is, the generator/captor 62 a converts rays of visible lightreflected from the object 60 into the optical signal, which propagatesthrough the cable 58. The generator/captor 62 a may couple the reflectedlight rays directly into the cable 58 as the optical signal. Or, thegenerator/captor 62 a may conventionally convert the wavelength set ofthe reflected light rays into a different wavelength set, and couplethis different wavelength set into the cable 58 as the optical signal.Alternatively, the cable 58 may convert the wavelength set of thereflected light rays into a different wavelength set. The optical signalbecomes the image beam 42 b, which the generator/captor 62 b scansacross the screen 34 b, along with the erase beam 52 b, to generate theimage 59. If the optical signal has a different wavelength set than theimage beam 42 b, then the generator/captor 62 b converts the opticalsignal into the desired wavelength set, and forms the image beam 42 bfrom the converted optical signal. So that it directs the image beam 42b onto the proper region 44 b on the screen 34 b at the proper time, thegenerator/captor 62 b is synchronized to the generator/captor 62 a.Techniques for performing such synchronization are discussed in commonlyowned U.S. patent application Ser. No. 09/129,739, entitled “LinkedScanner Imaging System And Method”, which is heretofore incorporated byreference.

[0044] The system 55 b is similar to the system 55 a and includes theimage generator/captor 62 b, which scans an erase beam 52 b and theimage beam 42 b across the screen 34 b to generate the image 59 in amanner similar to that described above in conjunction with FIG. 2. Asdiscussed above, the image generator/captor 62 a scans the object 60 togenerate the image beam 42 b, which propagates to the generator/captor62 b via the cable 58. The generator/captor 62 b also captures the image56 by scanning rays of light reflected from the object 61 into the cable58 as an optical signal as discussed above. This optical signal becomesthe image beam 42 a, which the generator/captor 62 a scans across thescreen 34 a, along with the erase beam 52 a, to generate the image 56.

[0045] Still referring to FIG. 3, in operation of the optical-linkedimaging system 54, the image generator/captor 62 a simultaneouslycaptures the image 59 and generates the image 56 on the screen 34 a.More specifically, the generator/captor 62 a simultaneously scans theimage 59 of the object 60 into the cable 58, and scans the image beam 42a from the cable 58 and the erase beam 52 a across the screen 34 a. Theilluminator 24 a illuminates the screen 34 a as described above inconjunction with FIG. 1 such that the screen 34 a displays/projects theimage 56. Similarly, the image generator/captor 62 b simultaneouslycaptures the image 56 of the object 61 and generates the image 59 on thescreen 34 b. More specifically, the generator/captor 62 b simultaneouslyscans the image 56 of the object 61 into the cable 58, and scans theimage beam 42 b from the cable 58 and the erase beam 52 b across thescreen 34 b. The illuminator 24 b illuminates the screen 34 b asdescribed above in conjunction with FIG. 1 such that the screen 34 bdisplays/projects the image 59. Because of the known properties andbehaviors of electromagnetic waves, the optical signal representing thecaptured image 56 does not significantly interfere with the opticalsignal representing the captured image 59 as these optical signalspropagate in opposite directions through the cable 58.

[0046] To increase the signal strength, one may amplify the opticalsignals as they propagate through the cable 58. For example, one may useone or more erbium-doped fiber amplifiers (not shown) to amplify one orboth of the optical signals. Examples of erbium-doped fiber amplifiersare discussed in U.S. Pat. Nos. 5,027,079, entitled “Erbium-Doped FiberAmplifier,” and 6,094,298, entitled “Erbium-Doped Fiber Amplifier WithAutomatic Gain Control,” which are incorporated by reference.

[0047]FIG. 4A is a detailed view of the image generator/captor 62 a ofFIG. 3 according to an embodiment of the invention, and also includesthe image amplifier 22 a and the object 60 of FIG. 3. Although only thegenerator/captor 62 a is discussed in detail, it is understood that thegenerator/captor 62 b is similar.

[0048] The image generator/captor 62 a includes a sinusoidallyresonating mirror 70, an optical assembly 72 (represented by a lens), anerase-beam generator 74, and conventional beam splitters 75 and 77.Resonating mirrors such as the mirror 70 are discussed, e.g., incommonly owned U.S. patent application Ser. No. 09/129,739, entitled“Linked Scanner Imaging System And Method”, and U.S. Pat. No. 6,140,979,entitled “Scanned Display With Pinch, Timing, And DistortionCorrection”, which are heretofore incorporated by reference, andcommonly owned U.S. patent application Ser. Nos. 09/128,927, entitled“Real Time Millimeter Wave Scanning Imager”, 09/128,954, entitled“Personal Display With Vision Tracking”, 09/129,619, entitled “Low LightViewer With Image Simulation”, and 09/144,400, entitled “Scanned BeamDisplay”, which are incorporated by reference.

[0049] The mirror 70 resonates at a predetermined horizontal rate andoscillates at a predetermined vertical rate to scan the image and erasebeams 42 a and 52 a across the screen 34 a and to direct the light rays76—only one light ray 76 shown—reflected from the object 60 into thecable 58 via the assembly 72 as a continuous capture beam. The assembly72 and beam splitter 77 respectively direct the image and erase beams 42a and 52 a from the entry-exit point 79 and the generator 74 onto anincidence point 78—preferably the center point—of the mirror 70. As themirror moves horizontally and vertically, the angles of incidencebetween the beams 42 a and 52 a and the mirror 70 change such that thebeams 42 a and 52 a move across the screen 34 a in horizontal andvertical directions, and thus scan the image 56 onto the screen 34 a.Furthermore, the assembly 72 receives the light rays 76 as a single beamvia reflection from the incidence point 78. As the mirror 70 moveshorizontally and vertically, the angle of incidence between the incomingrays 76 and the mirror 70 changes. Therefore, although the rays 76originate from different points on the object 60 at different times,they always enter the assembly 72 at or approximately at the sameentry-exit point 79. Consequently, the mirror 70 scans the image 59(FIG. 3) of the object 60 into the entry-exit point 79.

[0050] The beam splitter 75 allows the single mirror 70 to scan theimage beam 42 a from the cable 58 onto the screen 34 a and tosimultaneously scan the ray 76 from the object 60 into the cable 58. Inmost embodiments of the system 55 a of FIG. 3, the image amplifier 22 aand the object 60 are at different angles with respect to the reflector70. Consequently, the beam splitter 75 allows both the image beam 42 aand the ray 76 to be coincident with a common point of the mirror70—here the center point 78—and thus with the end of the cable 58.Alternatively, one can cause the beam 42 a and the ray 76 to becoincident with the end of the cable 58 according to conventionaltechniques for providing a common focal point for multiple light beams.For example, such techniques are disclosed in U.S. Pat. Nos. 5,907,425and 6,007,208, which are both entitled “Miniature Scanning ConfocalMicroscope” and which are incorporated by reference.

[0051] The beam splitter 77 allows positioning of the beam 52 arelatively close to the beam 42 a on the screen 34 a despite theerase-beam generator 74 being relatively far away from the end of thecable 58. Alternatively, one can omit the splitter 77 by placing thegenerator 74 relatively close to the end of the cable 58 such that thebeams 42 a and 52 a are relatively close together. But because the beamdiameters are relatively small and the cable 58 and generator 74 arerelatively large, such relatively close placement, and thus eliminationof the splitter 77, is often impractical or impossible.

[0052] In operation, the image generator/captor 62 a simultaneouslygenerates the image 56 on the screen 34 a and captures the image 59(FIG. 3) of the object 60. The image beam 42 a, which the assembly 55 bgenerates as discussed above in conjunction with FIG. 3, enters theoptical assembly 72 from the cable 58, and the erase-beam generator 74generates the erase beam 52 a. The assembly 72 and the beam splitter 77respectively direct the beams 42 a and 52 a to the incidence point 78 ofthe mirror 70, which scans the beams 42 a and 52 a across the screen 34a. In addition, the rays 76 strike the incidence point 78 of the mirror70, which directs the rays 76 into the entry point 79 of the assembly 72along the same or approximately the same path as the beam 42 a. Theassembly 72 directs the rays 76 into the cable 58. As discussed above,the beam 42 a and rays 76—the assembly 55 b uses the continuous beamformed by the rays 76 as the image beam 42 b—do not significantlyinterfere with one another as they propagate in opposite directionsthrough the cable 58.

[0053] Still referring to FIG. 4A, although shown as having a singlemirror 70, the image generator/captor 62 a may include multiple mirrors.For example, the generator/captor 62 a may include a pair of mirrors,one for the image and erase beams 42 a and 52 a and one for the lightrays 76. In such an embodiment, the mirrors can be positioned such thatthe beam splitter 75 can be omitted from the generator/captor 62 a.Furthermore, including only single mirrors 70 a and 70 b in thegenerator/captors 62 a and 62 b may prevent the mirrors 70 a and 70 bfrom being synchronized for both optical signals—one signal propagatingfrom the generator/captor 62 a to the generator/captor 62 b and viceversa. As discussed above, if the propagation delay of the opticalsignals is too long—this typically occurs when the cable 58 exceeds afew hundred feet—then the scanning angles of the mirrors 70 a and 70 bcan be offset with respect to each other to compensate for this delay,and to thus reduce or eliminate corruption of the respective scanned-outimage. But delay compensating for one scanned-out image often worsensthe delay corruption for the other image. For example, delaycompensating for the scanned-out image 56 may increase the corruption ofthe scanned-out image 59 (FIG. 3). One technique for preventing suchcorruption is to adjust the round-trip delay (e.g., from the mirror 70a, through the cable 58 to the mirror 70 b, back from the mirror 70 b,and through the cable 58 to the mirror 70 a) to equal an integermultiple of the time it takes to scan a horizontal line of the image 56or 59. Another technique is to use multiple mirrors as discussed above.This allows one to compensate for propagation delay in one directionindependently of the propagation delay in the other direction.

[0054]FIG. 4B is a detailed view of the image generator/captor 62 a ofFIG. 3 according to another embodiment of the invention, and, like FIG.4A, also includes the image amplifier 22 a and the object 60 of FIG. 3.The image generator/captor 62 a of FIG. 4B is similar to thegenerator/captor 62 a of FIG. 4A except that the beam splitter 77 iseffectively replaced with a conventional optical-signal combiner 80 anda conventional optical-beam separator 81. Although only thegenerator/captor 62 a is discussed in detail, it is understood that thegenerator/captor 62 b is similar.

[0055] The signal combiner 80 and beam separator 81 allow positioning ofthe erase beam 52 a with respect to the image beam 42 a without the beamsplitter 77. The combiner 80 combines the optical signal—which willbecome the image beam 42 a—and the erase beam 52 a from the erase-beamgenerator 74 such that the beams 42 a and 52 a exit the end 82 of thecombiner 80 and enter the beam separator 81 as collinear beams. In thisembodiment, the beams 42 a and 52 a have different wavelengths such thattheir respective angles of refraction with the separator 81 aredifferent. These different angles of refraction separate the beams by adistance d, which depends on the wavelengths of the beams 42 a and 52 a,the thickness and refractive index of the separator 81, and the angle ofthe separator 81 with respect to the collinear beams 42 a and 52 a. Inthe illustrated embodiment the optical assembly 72 is designed tomaintain this separation distance d, although in other embodiments theassembly 72 can be designed to increase or decrease d.

[0056] In operation, the image generator/captor 62 a simultaneouslygenerates the image 56 on the screen 34 a and captures the image 59(FIG. 3) of the object 60. The erase-beam generator 74 generates theerase beam, and the combiner 80 combines the erase beam 52 a with theimage beam 42 a. The beams 42 a and 52 a exit the end 82 and enter theseparator 81 collinearly. The separator 81 separates the beams 42 a and52 a. The optical assembly 72 respectively directs the beams 42 a and 52a to the incidence points 78 a and 78 b of the mirror 70, which scansthe beams 42 a and 52 a across the screen 34 a via the beam splitter 75.In addition, the rays 76 strike the incidence point 78 a of the mirror70, which directs the rays 76 into the entry point 79 a of the assembly72 along the same or approximately the same path as the beam 42 a. Theassembly 72 directs the rays 76 into the cable 58 via the separator 81and combiner 80.

[0057] Still referring to FIG. 4B, as discussed above in conjunctionwith FIG. 4A, the generator/captor 62 a may include a pair of mirrors,one for the image and erase beams 42 a and 52 a and one for the lightrays 76.

[0058] FIGS. 5-12 are embodiments of erase-beam/image-beam/capture-beamscanning assemblies that image generators or image generators/captorssuch as the generator 52 (FIG. 2) or the generators/captors 62 a and 62b (FIGS. 3-4) can incorporate. For clarity of explanation, the lightrays 76—which form at least one capture beam—of FIG. 4 are omitted fromFIGS. 5-12, and a portion of an image amplifier 22 is included in FIGS.5-12. These scanning assemblies may receive the image beams 42 from afiber-optic cable such as the cable 58 (FIGS. 3-4), or may generate theimage beams 42 from electronic image data or according to othertechniques. Furthermore, the scanning assemblies that generate and scanmultiple image beams 42 may use time-division-multiplexing or otherelectronic techniques to generate these multiple image beams from amaster image beam. Or, these scanning assemblies may receive themultiple image beams from another source or generate them fromelectronic image data.

[0059]FIG. 5 is a unidirectional, single-mirror,single-erase-beam/single-image-beam scanning assembly 82 according to anembodiment of the invention. The assembly 82 includes an image generator84 for generating the image and erase beams 42 and 52, and includes amirror assembly 86 for scanning the beams 42 and 52 across the screen 34in a sinusoidal scan pattern 88. During the scan from left to right inthe horizontal (H) direction, the generator activates both the image anderase beams 42 and 52 such that the erase beam 52 leads the image beam42 as described above in conjunction with FIG. 2. So that the erase beam52 does not lag the image beam 42, the generator 84 deactivates thebeams 42 and 52 during the scan from right to left, which is oftencalled the fly-back scan. Sinusoidal scanning techniques that aresimilar to the described technique are disclosed in U.S. Pat. No.6,140,979, entitled “Scanned Display With Pinch, Timing, And DistortionCorrection”, and commonly owned U.S. patent application Ser. Nos.09/128,927, entitled “Real Time Millimeter Wave Scanning Imager”,09/129,739, entitled “Linked Scanner Imaging System And Method”,09/128,954, entitled “Personal Display With Vision Tracking”,09/129,619, entitled “Low Light Viewer With Image Simulation”, and09/144,400, entitled “Scanned Beam Display”, which are heretoforeincorporated by reference.

[0060] Still referring to FIG. 5, in one embodiment the mirror assembly86 is a micro-electromechanical (MEM) mirror assembly having a mirror90, which pivots back and forth in the horizontal direction on torsionarms 92 a and 92 b and in the vertical (V) direction on torsion arms 94a and 94 b to scan the beams 42 and 52. Typically, the beams 42 and 52are incident on a center point 96 of the mirror 90, although the beamsmay be incident on another point of the mirror 90. An electronic signalapplied to electrodes (not shown) respectively maintains the horizontalpivot of the mirror 90 at a horizontal resonant scanning frequency thatis a function of the mirror dimensions, torsion arm dimensions (92 a and92 b), and other parameters of the mirror assembly 86. Alternatively,the horizontal scanner frequency may not be the resonant horizontalscanning frequency. A steady-state magnetic filed generated by magnets(not shown) and an alternating magnetic field generated by acurrent-carrying coil (not shown) on a gimbal maintain the verticalpivot of the mirror 90 at a vertical scanning frequency. Because thevertical scanning frequency is relatively low, it may not be theresonant vertical frequency of the mirror assembly 86. Alternatively,the mirror 90 may be electro-magnetically driven in the horizontaldirection, or electrostatically in the vertical direction. Othertechniques such as piezoelectric or bimorphic techniques may also beused to drive the mirror 90 horizontally or vertically. MEM mirrorassemblies such as the assembly 86 are discussed in U.S. Pat. Nos.5,629,790, entitled “Micromachined Torsional Scanner” to Neukermans etal. and 6,140,979, entitled “Scanned Display With Pinch, Timing, AndDistortion Correction”, and in commonly owned U.S. patent applicationSer. Nos. 09/128,927, entitled “Real Time Millimeter Wave ScanningImager”, 09/128,954, entitled “Personal Display With Vision Tracking”,09/129,619, entitled “Low Light Viewer With Image Simulation”, and09/144,400, entitled “Scanned Beam Display”, which are heretoforeincorporated by reference. In another embodiment, the mirror assembly 86is a mechanical assembly such as disclosed in commonly owned U.S. patentapplication Ser. No. 09/129,739, entitled “Linked Scanner Imaging SystemAnd Method”, which is heretofore incorporated by reference.

[0061] In operation, the mirror 90 of the mirror assembly scans theactive beams 42 and 52 across the screen 34 from left to right, andscans the inactive beams 42 and 52 across the screen 34 from right toleft. During a left-to-right scan, the image generator 84 activates thebeams 42 and 52 and directs them to the incidence point 96. The mirror90 pivots from left to right to scan the active beams 42 and 52 acrossthe screen 34 and to thus generate an image (not shown). In theillustrated embodiment, the mirror 90 scans the beams 42 and 52 past theright edge of the screen 34. This over scanning helps to avoid rasterpinch, which is an undesirable result of sinusoidal scanning asdiscussed in U.S. Pat. No. 6,140,979, entitled “Scanned Display WithPinch, Timing, And Distortion Correction”, which is heretoforeincorporated by reference. For unidirectional writing (i.e., where thebeam 42 is inactive during the fly-back scan), raster pinch is typicallynot a problem. Therefore, other embodiments the mirror 90 may not overscan the beams 42 and 52. When the mirror 90 pivots to its rightmostposition—or to another predetermined rightward position such as the beam42 reaching the right edge of the screen 34—the generator 84 deactivatesthe beams 42 and 52 for the fly-back scan. In one embodiment, the arms92 a and 92 b produce voltages that are proportional to the horizontalpivot position of the mirror 90. Torsion arms that produce such voltagesare discussed in U.S. Pat. No. 5,648,618, entitled “Micromachined HingeHaving An Integral Torsion Sensor” to Neukermans et al., which isincorporated by reference. By monitoring these voltages, circuitry (notshown) can cause the generator 84 to deactivate the beams 42 and 52 atthe desired time. The mirror 90 then scans the inactive beams 42 and 52from right to left across the screen 34. When the mirror 90 reaches adesired leftward rotational position, the generator 84 activates thebeams 42 and 52 for the next left-to-right scan.

[0062] During this horizontal scanning, the mirror 90 is also pivotingon the arms 94 a and 94 b via the gimbal ring to vertically scan thescreen 34 from top to bottom. Once the mirror 90 reaches its bottommostposition, it begins pivoting toward its top position. During this upwardpivot, the mirror 90 may continue to scan the beams 42 and 52 in thehorizontal direction as described above. Or, the image generator 84 maydeactivate the beams 42 and 52 until the mirror 90 reaches its topmostposition, and then activate the beams as described above to scan theimage during the mirror's top-to-bottom pivot. Alternatively, the mirror90 may scan the image during the mirror's bottom-to-top pivot only.

[0063] Alternate embodiments of the scanning assembly 82 are alsocontemplated. For example, the beams 42 and 52 may be generated byseparate image generators instead of a single image generator 84. Inaddition, the generator 84 may activate the beam 52 during the fly-backscan to erase the screen 34 between the lines scanned with the imagebeam 42. Furthermore, the assembly 82 may include two reflectors 86, oneto scan the image beam 42 and the other to scan the erase beam 52.Moreover, the assembly 82 may scan the beams 42 and 52 in a patternother than the sinusoidal pattern 88.

[0064]FIG. 6 is a unidirectional, single-mirror,multi-erase-beam/multi-image-beam scanning assembly 98 according to anembodiment of the invention. One difference between the scanningassemblies 82 (FIG. 5) and 98 is that the assembly 98 scans more thanone pair—two pairs in the illustrated embodiment—of image and erasebeams 42 and 52. Thus, the assembly 98 can increase the resolution ofthe scanned image (not shown) for a given horizontal scan rate (thehorizontal pivoting speed of the mirror 90).

[0065] The scanning assembly 98 includes a first image generator 100 forgenerating the image and erase beams 42 a and 52 a, and includes asecond image generator 102 for generating the image and erase beams 42 band 52 b. In one embodiment, the generators 100 and 102 are similar tothe image generator 84 (FIG. 5). The remaining elements of the assembly98 are the same as or similar to the elements of the scanning assembly82 (FIG. 5). During the scan from left to right in the horizontaldirection, the generators 100 and 102 respectively activate the imageand erase beams 42 a, 52 a, 42 b, and 52 b such that the erase beams 52a and 52 b respectively lead the image beams 42 a and 42 b as describedabove in conjunction with FIG. 2. So that the erase beams 52 a and 52 bdo not lag the image beams 42 a and 42 b, the generators 100 and 102deactivate the beams 42 a, 52 a, 42 b, and 52 b during the fly-back scanfrom right to left.

[0066] Still referring to FIG. 6, the scanning assembly 98 operates in amanner that is similar to the manner in which the scanning assembly 82(FIG. 5) operates. Specifically, the mirror 90 scans the active beams 42a, 52 a, 42 b, and 52 b across the screen 34 from left to right, andscans the inactive beams 42 a, 52 a, 42 b, and 52 b across the screen 34from right to left. During a left-to-right scan, the beam generators 100and 102 activate the beams 42 a, 52 a, 42 b, and 52 b and direct them tothe incidence point 96. The mirror 90 pivots from left to right to scanthe active beams 42 a, 52 a, 42 b, and 52 b across the screen 34 and tothus generate an image (not shown). When the mirror 90 pivots to itsrightmost position—or to another predetermined rightward position suchas the beams 42 a and 42 b reaching the right edge of the screen 34—thebeam generators 100 and 102 deactivate the beams 42 a, 52 a, 42 b, and52 for the fly-back scan. The mirror 90 then scans the inactive beams 42a, 52 a, 42 b, and 52 b from right to left across the screen 34. Whenthe mirror 90 reaches a desired leftward rotational position, thegenerators 100 and 102 activate the beams 42 a, 52 a, 42 b, and 52 b forthe next left-to-right scan.

[0067] During this horizontal scanning procedure, the mirror 90 is alsopivoting on the arms 94 a and 94 b via the gimbal ring 97 to verticallyscan the screen 34 from top to bottom. Once the mirror 90 reaches itsbottommost position, it begins pivoting toward its top position. Duringthis upward pivot, the mirror 90 may continue to scan the beams 42 a, 52a, 42 b, and 52 b in the horizontal direction as described above. Or,the generators 100 and 102 may respectively deactivate the beams 42 a,52 a, 42 b, and 52 b until the mirror 90 reaches its topmost position,and then activate the beams as described above to scan the image duringthe mirror's top-to-bottom pivot. Alternatively, the mirror 90 may scanthe image during the mirror's bottom-to-top pivot only.

[0068] Alternate embodiments of the scanning assembly 98 arecontemplated. For example, the beams 42 a, 52 a, 42 b, and 52 b may begenerated by separate image generators or by a single image generator.Or, the beams 42 a and 42 b may be generated by one generator, and thebeams 52 a and 52 b by another generator. In addition, the assembly 98may generate and scan more than two pairs of image and erase beams.Moreover, alternate embodiments similar to those discussed above inconjunction with FIG. 5 are contemplated where possible.

[0069]FIG. 7 is a unidirectional, single-mirrorwide-erase-beam/multi-image-beam scanning assembly 104 according to anembodiment of the invention. One difference between the scanningassemblies 98 (FIG. 6) and 104 is that the assembly 104 scans a single,wide erase beam 52 instead of multiple, narrow erase beams. Thus, theassembly 104 is often less complex and less expensive than the assembly98.

[0070] The scanning assembly 104 includes a first beam generator 106 forgenerating a wide erase beam 52, and includes a second beam generator108 for generating multiple image beams—here two—42 a and 42 b. Becauseconventional techniques, such as a laser with associated couplingoptics, exist for generating a wide optical beam, a detailed discussionof the generation of the wide erase beam 52 is omitted for clarity. Theremaining elements of the assembly 104 are the same as or similar to theelements of the scanning assembly 98 (FIG. 6). During the scan from leftto right in the horizontal direction, the generators 106 and 108respectively activate the wide erase beam 52 and the image beams 42 aand 42 b such that the erase beam 52 leads both the image beams 42 a and42 b as described above in conjunction with FIG. 2. The erase beam 52 iswide enough to simultaneously erase the paths that the image beams 42 aand 42 b will scan. So that the erase beam 52 does not lag the imagebeams 42 a and 42 b, the generators 106 and 108 respectively deactivatethe erase beam 52 and the image beams 42 a and 42 b during the fly-backscan from right to left.

[0071] Still referring to FIG. 7, the scanning assembly 104 operates ina manner that is similar to the manner in which the scanning assembly 98(FIG. 6) operates. Specifically, the mirror 90 scans the active beams 42a, 42 b, and 52 across the screen 34 from left to right, and scans theinactive beams 42 a, 42 b, and 52 across the screen 34 from right toleft. During a left-to-right scan, the beam generators 106 and 108respectively activate the erase beam 52 and the image beams 42 a and 42b and direct them to the incidence point 96. The mirror 90 pivots fromleft to right to scan the active beams 42 a, 42 b, and 52 across thescreen 34 and to thus generate an image (not shown). When the mirror 90pivots to its rightmost position—or to another predetermined rightwardposition such as the beams 42 a and 42 b reaching the right edge of thescreen 34—the beam generators 106 and 108 respectively deactivate theerase beam 52 and the image beams 42 a and 42 b for the fly-back scan.The mirror 90 then scans the inactive beams 42 a, 42 b, and 52 fromright to left across the screen 34. When the mirror 90 reaches a desiredleftward rotational position, the generators 106 and 108 respectivelyactivate the beams 42 a, 42 b, and 52 for the next left-to-right scan.

[0072] During this horizontal scanning procedure, the mirror 90 is alsopivoting on the arms 94 a and 94 b to vertically scan the screen 34 fromtop to bottom. Once the mirror 90 reaches its bottommost position, itbegins pivoting toward its top position. During this upward pivot, themirror 90 may continue to scan the beams 42 a, 42 b, and 52 in thehorizontal direction as described above. Or, the generators 106 and 108may respectively deactivate the erase beam 52 and the image beams 42 aand 42 b until the mirror 90 reaches its topmost position, and thenactivate the beams as described above to scan the image during themirror's top-to-bottom pivot. Alternatively, the assembly 104 mayperform the scanning of the image during the mirror's bottom-to-toppivot only.

[0073] Alternate embodiments of the scanning assembly 104 arecontemplated. For example, the beams 42 a, and 42 b may be generated byseparate image generators. Or, a single generator may generate the beams42 a, 42 b, and 52. In addition, alternate embodiments similar to thosediscussed above in conjunction with FIGS. 5-6 are contemplated wherepossible. FIG. 8 is a unidirectional, tiling, multi-mirror,multi-erase-beam/multi-image-beam scanning assembly 110 according to anembodiment of the invention. The assembly 110 includes multiple scanningassemblies 98 a-98 d—only 98 a and 98 b are shown for clarity—which areeach similar to the scanning assembly 98 (FIG. 6) and which each scan aportion of an image (not shown) onto a respective section, i.e., tile,112 a-112 d of the screen 34. Scanning portions of an image ontorespective screen tiles is often called “tiling”. Tiling typicallyinvolves simultaneously scanning a plurality of screen tiles, althoughin some applications, single tile may be scanned, or multiple tiles maybe scanned one at a time. By scanning a plurality of tilessimultaneously, the assembly 110 can increase the resolution of thescanned image for a given horizontal scan rates of the mirrors 90 a-90d. Furthermore, to allow horizontal over scanning for reducing rasterpinch, a gap 114 may be included between horizontally adjacent tiles 112of the screen 34. The gap 114 is typically wide enough to allow overscanning of one tile 112 without scanning a horizontally adjacent tile112. For example, the gap 114 is typically wide enough to allow theimage beams 42 aa and 42 ba to over scan the tile 112 a without strikingthe tile 112 d. Alternatively, instead of including a gap 114, thescreen may include a “dead” strip having the same width as the gap 114.The dead strip is a portion of the screen on which no portion of theimage is scanned.

[0074] Still referring to FIG. 8, with respect to the screen tiles 112a-112 d, each of the scanning assemblies 98 a-98 d operates in a mannerthat is similar to the manner in which the scanning assembly 98 (FIG. 6)operates as discussed above. One potential difference in operation,however, is that depending on the width of the gap 114 and how far tothe right the mirrors 90 a and 90 b respectively scan the image beams 42aa, 42 ba, 42 ab, and 42 bb, the generators 100 a, 102 a, 100 b, and 102b may deactivate the erase beams 52 aa, 52 ba, 52 ab, and 52 bb beforedeactivating the beams 42 aa, 42 ab, 42 ba, and 42 bb to prevent thebeams 52 aa, 52 ba, 52 ab, and 52 bb from respectively striking thetiles 112 d and 112 c.

[0075] Alternate embodiments of the scanning assembly 110 arecontemplated. For example, the screen 34 may be divided into more orfewer than four tiles 112. In addition, each scanning assembly 98 maysimultaneously scan multiple tiles. Furthermore, the assembly 110 mayinclude one or more of the scanning assemblies 82 (FIG. 5) or thescanning assemblies 104 (FIG. 7)—and implement the scanning techniquesassociated with these assemblies—in addition to or in place of thescanning assemblies 98. Moreover, alternate embodiments similar to thosediscussed above in conjunction with FIGS. 5-7 are contemplated wherepossible. In addition, because the gap 114 may cause artifacts in thescanned image, one may eliminate the gap 114 and turn the image anderase beams 42 and 52 off when they reach an edge of a tile 112.Consequently, even if the beams 42 and 52 over scan the tile 112, theywill not corrupt the image being scanned onto an adjacent tile 112.Alternatively, because they typically scan the same portion of an imageonto the same region of a tile 112, the beams 42 may over scan the edgesof adjacent tiles 112 without causing artifacts in the scanned image.But because the pixels in these over-scan regions may be scannedmultiple times per vertical scan, one may adjust the intensity of thebeams 42 in these over-scan regions such that the image is notnoticeably brighter in the over-scan regions as compared to thenon-over-scan regions. Furthermore, to avoid turning off the erase beams52 in the over-scan regions, one can design the assembly 110 such thatthe erase beams 52 lead the respective image beams 42 by one or morehorizontal lines as discussed below in conjunction with FIG. 12. FIG. 9is a unidirectional, tiling, single-mirror,multi-erase-beam/multi-image-beam scanning assembly 116 according to anembodiment of the invention. The assembly 116 is similar to the assembly110 (FIG. 8) except that it includes a scanning assembly 118, which is amodified version of the scanning assembly 98 (FIG. 6). Specifically, theassembly 118 includes a single mirror assembly 86 for scanning all ofthe beams 42 and 52 across all of the tiles 112 a-112 d. (For clarity,the beams 42 and 52 that scan the tiles 112 c-112 d are omitted.)Therefore, because it includes fewer mirror assemblies 86, the assembly116 is often less complex and less expensive than the assembly 110. Theparticular geometry for the mirror assembly 86 of the scanning assembly86 and other components will vary depending upon the application.However, some geometries for tiling with a single scanner are describedin commonly owned U.S. patent application Ser. No. 09/369,673, entitled“Scanned Display With Variation Compensation”, which is incorporated byreference.

[0076] Alternate embodiments of the scanning assembly 116 arecontemplated. For example, the assembly 116 may include a single imagegenerator to generate all of the beams 42 and 52, or may include imagegenerators that each generate more than one but fewer than all pairs ofthe beams 42 and 52. In addition, the assembly 116 may include modified(to generate the desired number of beams 42 and 52) versions of thescanning assemblies 82 (FIG. 5) or the scanning assemblies 104 (FIG.7)—and implement the scanning techniques associated with theseassemblies—in addition to or in place of the scanning assembly 118.Moreover, alternate embodiments similar to those discussed above inconjunction with FIGS. 5-8 are contemplated where possible.

[0077]FIG. 10 is a bidirectional, tiling, single-mirror,multi-erase-beam/multi-image-beam scanning assembly 120 according to anembodiment of the invention. Unlike the scanning assemblies of FIGS.5-9, the assembly 120 implements a bidirectional sinusoidal scanningpattern 122 to scan an image onto the screen 34 in both theleft-to-right and the right-to-left horizontal directions. For clarity,the sinusoidal pattern 122 is shown having straight scan paths and thefly-back scan paths are omitted. A similar bidirectional scanningtechnique is discussed in commonly owned U.S. patent application Ser.No. 09/370,790, entitled “Scanned Imaging Apparatus With SwitchedFeeds”, which is incorporated by reference.

[0078] The assembly 120 includes the single mirror assembly 86 forbidirectionally scanning multiple pairs of image and erase beams 42 and52 across multiple tiles 112 of the screen 34, and includes beamgenerators 100 a, 102 a, 100 b, and 102 b for respectively generatingthese beam pairs. More specifically, the mirror 90 scans active beams 42aa, 52 aa, 42 ab, and 52 ab across the tile 112 a while the mirror 90pivots horizontally from left to right, and scans active beams 42 ba, 52ba, 42 bb, and 52 bb across the tile 112 b while the mirror 90 pivotshorizontally from right to left. The erase beams 52 aa, 52 ab, 52 ba,and 52 bb are positioned such that they respectively lead the imagebeams 42 aa, 42 ab, 42 ba, and 42 bb across the tiles 112 a and 112 b.The optional gap or dead strip 114 allows over scanning withoutundesirable scanning of the adjacent tile 112. For example, the gap 114allows the mirror 90 to scan the beams 42 aa, 52 aa, 42 ab, and 52 abpast the right edge of the tile 112 a without striking the tile 112 bwith these beams. Alternatively, one can reduce the width of oreliminate the gap 14 by precisely calibrating the mirror 90 such thatthere is no over scanning of the tiles 112 a and 112 b.

[0079] In operation, the mirror 90 scans the active beams 42 aa, 42 ab,52 aa, and 52 ab across the tile 112 a from left to right, and scans theactive beams 42 ba, 42 bb, 52 ba, and 52 bb across the tile 112 b fromright to left. During a left-to-right scan, the beam generators 100 aand 102 a respectively activate the beams 42 aa, 52 aa, 42 ab, and 52 bband direct them to the incidence point 96, and the beam generators 100 band 102 b respectively deactivate the beams 42 ba, 52 ba, 42 bb, and 52bb. When the mirror 90 pivots to its rightmost position—or to anotherpredetermined rightward position such as the beams 42 aa and 42 abreaching the right edge of the tile 112 a—the generators 100 a and 102 arespectively deactivate the beams 42 aa, 52 aa, 42 ab, and 52 ab, andthe generators 100 b and 102 b respectively activate the beams 42 ba, 52ba, 42 bb, and 52 bb for the right-to-left scan. Depending on the widthof the gap 114 and how far to the right the mirror 90 scans the imagebeams 42 aa and 42 ba, the generators 100 a and 102 a may deactivate theerase beams 52 aa and 52 ba before deactivating the beams 42 aa and 42ba to prevent the beams 52 aa and 52 ba from striking the tile 112 b.The mirror 90 then scans the active beams 42 ba, 52 ba, 42 bb, and 52 bbfrom right to left across the tile 112 b. When the mirror 90 reaches adesired leftward rotational position, the generators 100 a and 102 arespectively activate the beams 42 aa, 52 aa, 42 ab, and 52 ab and thegenerators 100 b and 102 b respectively deactivate the beams 42 ba, 52ba, 42 bb, and 52 bb for the next left-to-right scan of the tile 112 a.Depending on the width of the gap 114 and how far to the left the mirror90 scans the image beams 42 ba and 42 bb, the generators 100 b and 102 bmay deactivate the erase beams 52 ba and 52 bb before deactivating thebeams 42 ba and 42 bb to prevent the beams 52 ba and 52 bb from strikingthe tile 112 a.

[0080] During this bidirectional horizontal scanning procedure, themirror 90 is also pivoting vertically to scan the tiles 112 a and 112 bfrom top to bottom. Once the mirror 90 reaches its bottommost position,it begins pivoting toward its top position. During this upward pivot,the mirror 90 may continue to scan the beams 42 aa, 52 aa, 42 ab, 52 ab,42 ba, 52 ba, 42 bb, and 52 bb in the horizontal direction as describedabove. Or, the generators 100 a, 102 a, 100 b, and 102 b deactivate thebeams until the mirror 90 reaches its topmost position, and thenactivate the beams as described above to scan the image during themirror's top-to-bottom pivot. Alternatively, the mirror 90 may scan theimage during its bottom-to-top pivot only.

[0081] Alternative embodiments of the scanning assembly 120 arecontemplated. For example, one can modify the assembly 120 to scan moreor fewer than two pairs of image and erase beams, to implement thewide-erase-beam technique of FIG. 7, or to implement the multiple-mirroror no-gap techniques of FIG. 8.

[0082]FIG. 11 is a bidirectional, single-mirror,multi-erase-beam/multi-image-beam scanning assembly 124 according to anembodiment of the invention. The assembly 124 is similar to the scanningassembly 120 of FIG. 10 except that it scans an image onto the samesection of the screen 34 during both the left-to-right and right-to-lefthorizontal scans. Therefore, for the same horizontal scan rate, theassembly 124 often generates a higher-resolution image than the assembly120 or the scanning assemblies of FIGS. 5-9. To ensure that an erasebeam 52 leads an image beam 42 in both horizontal scanning directions,beam generators 126 a and 126 b each generate two erase beams 52 perimage beam 42, one erase beam for the left-to-right scan and one erasebeam for the right-to-left scan.

[0083] The assembly 124 includes a single mirror assembly 86 forbidirectionally scanning multiple trios of image and erase beams 42 a,52 aa, and 52 ab and 42 b, 52 ba, and 52 bb across the screen 34, andincludes the beam generators 126 a and 126 b for respectively generatingthese beam trios. More specifically, the mirror 90 scans the activebeams 42 a and 52 ab and 42 b and 52 bb across the screen 34 while themirror 90 pivots horizontally from left to right—the generators 126 aand 126 b deactivate the erase beams 52 aa and 52 ba during theleft-to-right scan—and scans active beams 42 b, 52 aa, and 52 ba acrossthe screen 34 while the mirror 90 pivots horizontally from right toleft—the generators 126 a and 126 b deactivate the erase beams 52 ab and52 bb during the right-to-left scan. Because the mirror 90 scans theimage onto the screen 34 in both horizontal directions, raster pinch,which is an undesirable occurrence discussed in heretofore incorporatedU.S. Pat. No. 6,140,979, entitled “Scanned Display With Pinch, Timing,And Distortion Correction”, may be a problem. Therefore, to reduce oravoid the problems associated with raster pinch, in the illustratedembodiment the mirror 90 over scans the image beams 42 a and 42 b pastboth the left and right edges of the screen 34. U.S. Pat. No. 6,140,979,entitled “Scanned Display With Pinch, Timing, And DistortionCorrection”, also discusses other techniques for reducing or eliminatingthe affects of raster pinch, and one can modify the assembly 124 toimplement one or more of these techniques.

[0084] Still referring to FIG. 11, in operation the mirror 90 scans theactive beams 42 a, 42 b, 52 ab, and 52 bb across the screen 34 from leftto right, and scans the active beams 42 a, 42 b, 52 aa, and 52 ba acrossthe screen 34 from right to left. During a left-to-right scan, the beamgenerators 126 a and 126 b respectively activate the beams 42 a, 52 ab,42 b, and 52 bb and direct them to the incidence point 96, andrespectively deactivate the beams 52 aa and 52 ba. When the mirror 90pivots to its rightmost position—or to another predetermined rightwardposition such as the inactive beams 52 aa and 52 ba reaching the rightedge of the screen 34—the generators 126 a and 126 b respectivelydeactivate the beams 52 ab and 52 bb and respectively activate the beams42 a, 52 aa, 42 b, and 52 ba for the right-to-left scan. The mirror 90then scans the active beams 42 a, 52 aa, 42 b, and 52 ba from right toleft across the screen 34. When the mirror 90 reaches a desired leftwardrotational position, the generators 126 a and 126 b respectivelyactivate the beams 42 a, 52 ab, 42 b, and 52 bb and respectivelydeactivate the beams 52 aa and 52 ba for the next left-to-right scan ofthe screen 34.

[0085] During this bidirectional horizontal scanning procedure, themirror 90 is also pivoting vertically to scan the screen 34 from top tobottom. Once the mirror 90 reaches its bottommost position, it beginspivoting toward its top position. During this upward pivot, the mirror90 may continue to scan the beams 42 a, 42 b, 52 aa, 52 ab, 52 ba, and52 bb in the horizontal directions as described above. Or, thegenerators 126 a and 126 b may deactivate the beams until the mirror 90reaches its topmost position, and then activate the beams as describedabove to scan the image during the mirror's top-to-bottom pivot.Alternatively, the mirror 90 may scan the image during its bottom-to-toppivot only.

[0086] Alternative embodiments of the scanning assembly 124 arecontemplated. For example, one can modify the assembly 124 to scan moreor fewer than two trios of image and erase beams, to implement themultiple-mirror technique of FIG. 8., to implement the tiling techniquesof FIGS. 8 and 9, or to implement the switched scanning technique ofFIG. 10. In addition, one can modify the assembly 124 according to thetechnique of FIG. 7 by replacing the beams 52 aa and 52 ba with a firstwide erase beam and by replacing the beams 52 ba and 52 bb with a secondwide erase beam.

[0087] One potential problem with the bidirectional, multi-beam scanningtechnique of FIG. 11 is that the beams 52 aa and 52 ab may crossover,and thus erase, portions of lines scanned by the image beam 42 b. Thesecrossover points are typically near the edges of the screen 34. Forexample, near the beginning of a left-to-right scan, the beam 52 ab maycrossover a points of the previous line scanned by the beam 42 b nearthe left edge of the screen 34. Similarly, near the beginning of aright-to-left scan, the beam 52 aa may crossover a point of the previousline scanned by the beam 42 b near the right edge of the screen 34.These erased crossover points may form artifacts that degrade thescanned image.

[0088] One solution to this crossover problem is to increase thedistances that the beams 42 and 52 over scan the right and left edges ofthe screen 34 such that the crossover points occur beyond the edges ofthe screen 34. Another solution is to eliminate the beams 52 aa and 52bb and make the beams 52 ba and 52 bb wide enough to erase the scan paththat the beam 42 a traverses. Yet another solution is to use an erasebeam 52 that leads the beam 42 b by one or more horizontal scan lines asdiscussed below in conjunction with FIG. 12.

[0089]FIG. 12 is a bidirectional, single-mirror,single-erase-beam/multi-image-beam scanning assembly 128 according to anembodiment of the invention. Unlike the scanning assemblies of FIGS.5-11 in which the erase beam leads the image beam by a distance d (FIG.2) of a few regions 44 in the same horizontal scan path, the erase beam52 of the assembly 128 leads the image beam or beams by at least onehorizontal scan line. Therefore, the assembly 128 need not activate anddeactivate the erase beam 52 after each horizontal scan like thebidirectional assemblies 120 and 124 (FIGS. 10-11).

[0090] The scanning assembly 128 includes a single mirror assembly 86for bidirectionally scanning one or more image beams—two image beams 42a and 42 b in the illustrated embodiment—and an erase beam 52, andincludes a beam generator 130 for generating these beams. The erase beam52 is at least one horizontal scan line ahead of the closest image beam42 b, typically far enough ahead so that it does not interfere with thebeam 42 b. More specifically, the mirror 90 scans the beams 42 a, 42 b,and 52 across the screen 34 while it pivots horizontally from left toright and from right to left. Because the mirror 90 scans the image ontothe screen 34 in both horizontal directions, raster pinch, which isdiscussed above in conjunction with e.g., FIG. 11, may be a problem.Therefore, to reduce or eliminate the problems associated with rasterpinch, in the illustrated embodiment the mirror 90 over scans the imagebeams 42 a and 42 b past both the left and right edges of the screen 34.

[0091] Still referring to FIG. 12, in operation the mirror 90 beginsscanning the beam 52 at the top of the screen 34 to erase the firsthorizontal scan line or lines, and then continues to scan the beams 42a, 42 b, and 52 downward and across the screen 34 from left to right andfrom right to left. The beam generator 130 activates the beams 42 a, 42b, and 52 and directs them to the incidence point 96 during both theleft-to-right and right-to-left scans. Once the mirror 90 reaches itsbottommost position, it begins pivoting toward its top position. Duringthis upward pivot, the generator 130 deactivates the beams 42 a, 42 b,and 52, and then activates them again during the downward pivot. Or, thegenerator 130 may deactivate the beam 52 and generate another erase beam52 (not shown) on top of the beams 42 a and 42 b so that the reflector36 can bidirectionally scan the image as described above during theupward pivot. This allows the mirror 90 to scan the image during boththe top-to-bottom and bottom-to-top pivots. Alternatively, the mirror 90may scan the image during its bottom-to-top pivot only.

[0092] Alternative embodiments of the scanning assembly 128 arecontemplated. For example, one can modify the assembly 128 to have moreor fewer than two image beams 42. By adding additional image beams 42,one can increase the resolution of the image generated by the assembly128 without increasing the horizontal scan rate of the mirror 90. Onecan also modify the assembly 128 to implement the tiling techniques ofFIGS. 8 and 9 or to implement the scanning technique of FIG. 10. Inaddition, one can modify the assembly 128 according to the technique ofFIG. 7 by replacing the narrow erase beam 52 with a wide erase beam.Furthermore, instead of using the erase beam 52, one can simultaneouslyerase an entire line or lines of the screen 34 with an array oferase-energy generators such as organic light-emitting devices (OLEDs).For example, the array can have rows of OLEDs, each row aligned with arespective line of the screen 34. To erase a line, one activates thecorresponding row of OLEDs for a predetermined time. OLEDs are discussedin U.S. Pat. No. 5,929,562, entitled “Organic Light-Emitting Devices”,which is assigned to Cambridge Display Technology Ltd. and which isincorporated by reference.

[0093]FIG. 13 is a top view of a color-image projection system 140according to an embodiment of the invention. The system 140 oftengenerates a higher-quality image and is often less expensive, lesscomplex, and more energy efficient than conventional image projectionssystems such as conventional projection television sets. Furthermore,although the system 140 is described as receiving and displaying videoframes, the system can receive and display still images as well.

[0094] The system 140 includes a conventional display screen 142 fordisplaying a color image, red, green, and blue image projectors 144_(R), 144 _(G), and 144 _(B), a scanning assembly 150 for scanning red,green, and blue portions of the image, and an electro/optical converter152 for respectively converting an electronic video signal into red,green, and blue optical scanning signals 154 _(R), 154 _(G), and 154_(B).

[0095] Each of the red, green, and blue image projectors 144 _(R), 144_(G), and 144 _(B) includes a respective image amplifier 22 _(R), 22_(G), and 22 _(B), a respective colored illumination source 160 _(R),160 _(G), and 160 _(B), and a respective optical assembly 162 _(R), 162_(G), and 162 _(B). The image amplifiers 22 _(R), 22 _(G), and 22 _(B)respectively include projection screens 34 _(R), 34 _(G), and 34 _(B)and are otherwise similar to the image amplifiers 22 of FIGS. 1-12. Theillumination sources 160 _(R), 160 _(G), and 160 _(B) respectivelyilluminate the screens 34 _(R), 34 _(G), and 34 _(B) with red, green,and blue light and are otherwise similar to the illumination source 24(FIGS. 1-3). The optical assemblies 162 _(R), 162 _(G), and 162 _(B)respectively receive the projected red, green, and blue image portionsfrom the screens 34 _(R), 34 _(G), and 34 _(B) and redirect theseprojected image portions onto the screen 142 to produce a color image.In one embodiment, the optical assemblies 162 _(R), 162 _(G), and 162_(B) magnify the red, green, and blue image portions so that displayedimage has desired dimensions. Because one can construct the opticalassemblies 162 _(R), 162 _(G), and 162 _(B) according to conventionaltechniques, the details of their structure and operation are omitted forbrevity.

[0096] The scanning assembly 150 respectively scans the red, green, andblue portions of the image onto the screens 34 _(R), 34 _(G), and 34_(B) according to any one of or a combination of the scanning techniquesand assemblies discussed above in conjunction with FIGS. 5-12. Forclarity, the described embodiment of the assembly 150 scans image beams42 _(R), 42 _(G), and 42 _(B) and erase beams 52 _(R), 52 _(G), and 52_(B) according to the unidirectional scanning technique discussed abovein conjunction with FIG. 5. For example, the assembly 150 scans thebeams 42 _(R) and 52 _(R) to generate on the screen 34 _(R) the imagepixels that have a red component to them. Likewise, the assembly 150scans the beams 42 _(G) and 52 _(G) to generate on the screen 34 _(G)the image pixels that have a green component to them, and scans thebeams 42 _(B) and 52 _(B) to generate on the screen 34 _(B) the imagepixels that have a blue component to them. In one embodiment, theassembly 150 respectively uses the optical signals 154 _(R), 154 _(G),and 154 _(B) as the image beams 42 _(R), 42 _(G), and 42 _(B). In otherembodiments, the assembly 150 conventionally converts the signals 154_(R), 154 _(G), and 154 _(B) into the beams 42 _(R), 42 _(G), and 42_(B), respectively.

[0097] The converter 152 is a conventional circuit for converting theconventional composite video signal into the red, green, and blueoptical signals 154 _(R), 154 _(G), and 154 _(B). For example, thecircuit 152 can separate the video signal into its red, green, and bluecomponents, and then, using lasers or laser diodes, convert the red,green, and blue components into the red, green, and blue optical signals154 _(R), 154 _(G), and 154 _(B). Because the image amplifiers 22 _(R),22 _(G), and 22 _(B) are monochrome amplifiers that are respectivelyilluminated with red, green, and blue light, neither the optical signals154 _(R), 154 _(G), and 154 _(B) nor the image beams 42 _(R), 42 _(G),and 42 _(B) need be colored.

[0098] Still referring to FIG. 13, in operation of the projection system140, the electro/optic signal converter 152 converts the received videosignal into red, green, and blue optical signals 154 _(R), 154 _(G), and154 _(B). The scanning assembly 150 converts these optical signals intothe respective image beams 42 _(R), 42 _(G), and 42 _(B), generates theerase beams 52 _(R), 52 _(G), and 52 _(B), and scans these beams acrossthe screens 34 _(R), 34 _(G), and 34 B to generate the respective red,green, and blue portions of the image. The illumination sources 160_(R), 160 _(G), and 160 _(B) respectively illuminate the screens 34_(R), 34 _(G), and 34 _(B) with red, green, and blue light such thatthese screens project the red, green, and blue image portions in theirrespective colors. The optical assemblies 162 _(R), 162 _(G), and 162_(B) respectively receive these projected color image portions andredirect them such that they are aligned, and thus form the color image,on the display screen 142. A viewer (not shown) can then view the colorimage on the screen 142. In one embodiment, a viewer views the colorimage from the front side—the side facing away from the opticalassemblies 162—of the screen 142.

[0099] Alternative embodiments of the projection system 140 arecontemplated. For example, the system 140 can be constructed so that aviewer views the image from the back side—the side facing the opticalassemblies 162—of the screen 142. Alternatively, the illuminationsources 160, the optical assemblies 162 and the screen 142 may belocated on the same side of the image amplifiers 22 as the scanningassembly 150, and the viewer may view the image from either side of thescreen 142. Furthermore, although the image amplifiers 22 _(R), 22 _(G),and 22 _(B) are shown as being separate and laterally spaced apart fromone another, they may be separate but contiguous with one another. Or,the image amplifiers 22 _(R), 22 _(G), and 22 _(B) may each compose arespective portion of a single piece. For example, the image amplifiers22 _(R), 22 _(G), and 22 _(B) may compose respective portions of asingle image amplifier (not shown).

[0100]FIG. 14 is a top view of a color-image projection system 170according to an embodiment of the invention. The system 170 is similarto the system 140 of FIG. 13 except that 1) the image projectors 144_(R) and 144 _(B) are angled more toward the screen 142 and 2) separatescanning assemblies 150 _(R), 150 _(G), and 150 _(B) respectively scanthe red, green, and blue image portions onto the screens 34 _(R), 34_(G), and 34 _(B). Alternatively, the system 170 may include a centralscanning assembly 150 like the system 140 does. Furthermore, because thescreens 34 _(R) and 34 _(B) of the system 170 have different angles withrespect to the display screen 142 as compared to the screens 34 _(R) and34 _(B) of the system 140, the optical assemblies 162 _(R) and 162 _(B)of the system 170 may be different than the optical assemblies 162 _(R)and 162 _(B) of the system 150.

[0101] In operation, the projection system 170 operates in a manner thatis similar to that described above for the projection system 140 of FIG.13.

[0102] Alternative embodiments of the projection system 170 arecontemplated. For example, the system 170 can be constructed so that aviewer views the image from the back side—the side facing the opticalassemblies 162—of the screen 142. Alternatively, the illuminationsources 160, the optical assemblies 162, and the screen 142 may belocated on the same side of the image amplifiers 22 as the scanningassembly 150, and the viewer may view the image from either side of thescreen 142. Furthermore, although the image amplifiers 22 _(R), 22 _(G),and 22 B are shown as being separate and laterally spaced apart from oneanother, they may be separate but contiguous with one another. Or, theimage amplifiers 22 _(R), 22 _(G), and 22 _(B) may each compose arespective portion of a single piece. For example, the image amplifiers22 _(R), 22 _(G), and 22 _(B) may compose respective portions of asingle image amplifier (not shown).

[0103] Referring to FIGS. 13 and 14, one can modify the projectionsystems 140 and 170 so that a viewer can view an image directly insteadof viewing the image on the screen 142. For example, one can modify theconstruction and positions of the optical assemblies 162, and insert anX cube (not shown) between the assemblies 162 and the viewer's eye (notshown). The X cube, which is generally four conventional prisms arrangedto form a cube, combines the color image portions from the assemblies162 into a viewable color image, and directs the image into the viewer'seye. The screen 142 may be omitted from such a direct-view system. Otheralternatives exist for converting the projection systems 140 and 170into direct-view systems. The details for converting the projectionssystems 140 and 170 into direct-view systems are known. Therefore, suchdetails are omitted for brevity.

[0104] From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention.

We claim:
 1. An image system, comprising: a projection screen includinga scan surface and a projection surface having a region of adjustablebrightness; and a beam generator operable to direct an electromagneticoff-beam and an electromagnetic on-beam onto the scan surface, theoff-beam operable to change the brightness of a region of the projectionsurface to a selected off-condition and the on-beam operable to changethe brightness of the region of the projection surface from the selectedoff-condition to a desired brightness level.
 2. The image system ofclaim 1 wherein: the scan surface is parallel to the projection surface;the beam generator is operable to direct the off-beam and on-beam onto aregion of the scan surface that is perpendicularly aligned orsubstantially perpendicularly aligned with the region of the projectionsurface.
 3. The image system of claim 1 wherein the beam generator isoperable to generate the on-and off-beams simultaneously.
 4. The imagesystem of claim 1 wherein the beam generator is operable to generate theon-and off-beams during non-overlapping time periods.
 5. The imagesystem of claim 1, further comprising: a display screen that faces theprojection surface of the projection screen; and wherein the projectionscreen is operable to project an image onto the display screen.
 6. Theimage system of claim 1 wherein: the projection surface has a pluralityof regions of adjustable brightness; the off-beam is operable to changethe respective brightness of each region of the projection surface tothe selected off-condition; and the on-beam is operable to change thebrightness of at least one of the regions of the projection surface to afirst brightness level that is different from the off condition and asecond of the regions of the projection surface to a second brightnesslevel different from the first brightness level and the off-condition inthe opposite direction.
 7. The image system of claim 1 wherein the scansurface is different from and faces away from the projection surface. 8.The image system of claim 1 wherein the scan surface and the projectionsurface are the same surface.
 9. An image system, comprising: a screenhaving a region responsive to electromagnetic energy to produce anadjustable brightness; and a beam generator operable to direct first andsecond electromagnetic beams onto the region, the first beam operable tochange the brightness of the region according to a first polarity andthe second beam operable to change the brightness of the regionaccording to a second polarity.
 10. The image system of claim 9 whereinthe beam generator is operable to direct the first beam onto the regionbefore directing the second beam onto the region.
 11. The image systemof claim 9 wherein the first beam is different than the second beam. 12.The image system of claim 9 wherein: the second beam has an intensity;and the second beam is operable to change the brightness of the regionto a brightness level that is related to the intensity.
 13. The imagesystem of claim 9 wherein: the second beam has a duration; and thesecond beam is operable to change the brightness of the region to abrightness level that is related to the duration.
 14. The image systemof claim 9 wherein the first beam has a different wave length than thesecond beam.
 15. The image system of claim 9 wherein: the first beam isoperable to decrease the brightness of the region; and the second beamis operable to increase the brightness of the region.
 16. The imagesystem of claim 9 wherein: the screen has multiple regions of adjustablebrightness; the beam generator is operable to direct the first andsecond beams onto the regions; the first beam is operable to change therespective brightnesses of the regions of the screen in the firstdirection; and the second beam is operable to change the brightness ofat least one of the regions of the screen in the second direction. 17.The image system of claim 9, further comprising an illuminator operableto illuminate the screen.
 18. An image system, comprising: a screenhaving a region with an adjustable reflectivity; and a beam generatoroperable to direct a first and second electromagnetic beams onto theregion, the first beam operable to change the reflectivity of the regionin a direction and the second beam operable to change the reflectivityof the region in an opposite direction.
 19. The image system of claim 18wherein: the second beam has an intensity; and the second beam isoperable to change the reflectivity of the region to a reflectivitylevel that is related to the intensity.
 20. The image system of claim 18wherein: the second beam has a duration; and the second beam is operableto change the reflectivity of the region to a reflectivity level that isrelated to the duration.
 21. The image system of claim 18, furthercomprising an illuminator operable to illuminate the screen.
 22. Theimage system of claim 18 wherein: the direction corresponds toincreasing the reflectivity of the region; and the opposite directioncorresponds to decreasing the reflectivity.
 23. The image system ofclaim 18 wherein: the projection screen has multiple regions ofadjustable reflectivity; the beam generator is operable to direct thefirst and second beams onto the regions; the first beam is operable tochange the respective reflectivities of the regions of the projectionscreen in the direction; and the second beam is operable to change thereflectivity of at least one of the regions of the projection screen inthe opposite direction.
 24. An image system, comprising: a projectionscreen having a scan surface and a projection surface that faces awayfrom the scan surface, the projection surface having a region ofadjustable reflectivity; and a beam generator operable to direct anelectromagnetic off beam and an electromagnetic on beam onto the scansurface, the off beam operable to change the reflectivity of a region ofthe projection surface in a first direction and the on beam operable tochange the reflectivity of the region of the projection surface in anopposite direction.
 25. The image system of claim 24 wherein: the scansurface is parallel to the projection surface; the beam scanner isoperable to direct the off beam and on beam onto a region of the scansurface that is perpendicularly aligned with the region of theprojection surface.
 26. The image system of claim 24, furthercomprising: an illuminator operable to illuminate the projection surfaceof the projection screen; a display screen that faces the projectionsurface of the projection screen; and wherein the projection screen isoperable to project an image onto the display screen.
 27. The imagesystem of claim 24 wherein: the projection surface has regions ofadjustable reflectivity; the off beam is operable to change therespective reflectivity of each region of the projection surface in afirst direction; and the on beam is operable to change the reflectivityof at least one of the regions of the projection surface in a seconddirection.
 28. A display, comprising: a screen having a region with anadjustable luminance; and a beam generator operable to direct anelectromagnetic erase beam and an electromagnetic image beam onto theregion, the erase beam operable to set the luminance of the region to apredetermined level and the image beam operable to change the luminanceof the region to a level other than the predetermined level.
 29. Thedisplay system of claim 28 wherein the beam generator is operable todirect the erase beam onto the region before directing the image beamonto the region.
 30. The display system of claim 28 wherein: the imagebeam has an intensity; and the image beam is operable to change theluminance of the region to a level that is related to the intensity. 31.The display system of claim 28 wherein: the image beam has a duration;and the image beam is operable to change the luminance of the region toa level that is related to the duration.
 32. The display system of claim28 wherein: the projection screen has multiple regions of adjustableluminance; the beam generator is operable to direct the erase beam andthe image beam onto the regions; the erase beam is operable to set therespective luminances of the regions of the projection screen to thepredetermined level; and the image beam is operable to change theluminance of at least one of the regions of the projection screen to thelevel other than the predetermined level.
 33. The display system ofclaim 28, further comprising an illuminator operable to illuminate theprojection screen.
 34. An image system, comprising: a projection screenhaving a scan surface and a projection surface that faces away from thescan surface, the projection surface having a region of adjustableluminance; and a beam generator operable to direct an electromagneticerase beam and an electromagnetic image beam onto the scan surface, theerase beam operable to set the luminance of the region of the projectionsurface to a predetermined level and the image beam operable to changethe luminance of the region of the projection surface to a level otherthan the predetermined level.
 35. The image system of claim 34 wherein:the scan surface is parallel to the projection surface; the beamgenerator is operable to direct the erase beam and image beam onto aregion of the scan surface that is perpendicularly aligned with theregion of the projection surface.
 36. The image system of claim 34wherein: the projection surface has multiple regions of adjustableluminance; the erase beam is operable to set the respective luminance ofeach region of the projection surface to the predetermined level; andthe image beam is operable to change the luminance of at least one ofthe regions of the projection surface to a level other than thepredetermined level.
 37. An image system, comprising: a screen having aregion with an adjustable luminance; and a light emitter operable todirect an erase light and a write light onto the region, the erase lightoperable to set the luminance of the region to a predetermined level andthe write light operable to change the luminance of the region to alevel other than the predetermined level.
 38. The image system of claim37 wherein the erase and write lights are visible.
 39. The image systemof claim 37 wherein the erase and write lights are invisible.
 40. Theimage system of claim 37 wherein the light emitter comprises an organiclight-emitting device that is operable to generate the erase light. 41.The image system of claim 37 wherein: the region comprises a line of thescreen; and the light emitter comprises a row of devices operable togenerate the erase light.
 42. The image system of claim 37 wherein: theregion comprises a line of the screen; and the light emitter comprises arow of organic light-emitting devices operable to generate the eraselight.
 43. An image system, comprising: a screen having a region with anadjustable luminance; and a light emitter operable to direct a firstlight at an erase wavelength and a second light at a write wavelengthonto the region, the first light operable to set the luminance of theregion to a predetermined level and the second light operable to changethe luminance of the region to a level other than the predeterminedlevel.
 44. The image system of claim 43 wherein the erase and writewavelengths are in a visible portion of the electromagnetic spectrum.45. The image system of claim 43 wherein the erase and write wavelengthsare in an invisible portion of the electromagnetic spectrum.
 46. Amethod, comprising: changing the brightness of a region of an imagescreen in an first direction with a first electromagnetic beam; andchanging the brightness of the region in an second direction with asecond electromagnetic beam.
 47. The method of claim 46, furthercomprising changing the brightness of the region of the image with thefirst beam before changing the brightness of the region with the secondbeam.
 48. The method of claim 46, further comprising simultaneouslygenerating the first and second beams.
 49. The method of claim 46wherein the first beam has a different characteristic than the secondbeam.
 50. The method of claim 46 wherein: changing the brightness of theregion in the first direction comprises decreasing the brightness of theregion; and changing the brightness of the region in the seconddirection comprises increasing the brightness of the region.
 51. Themethod of claim 46 wherein changing the brightness of the region in thesecond direction comprises setting the brightness of the region to alevel that is proportional to the intensity of the second beam.
 52. Themethod of claim 46 wherein changing the brightness of the region in thesecond direction comprises setting the brightness of the region to alevel that is proportional to the duration of the second beam.
 53. Themethod of claim 46, further comprising illuminating the region of thescreen.
 54. The method of claim 46 wherein the changing the brightnessof the region in the first direction comprises setting the brightness ofthe region to a predetermined level.
 55. The method of claim 46 wherein:changing the brightness of the region in the first direction comprisesscanning a scan surface of the image screen with the first beam; andchanging the brightness of the region in the second direction comprisesscanning the scan surface of the image screen with the second beam. 56.The method of claim 46, further comprising generating the first andsecond beams during different time periods.
 57. The method of claim 46wherein: changing the brightness of the region of the image screen inthe first direction comprises changing the reflectivity of the region inthe first direction with the first beam; and changing the brightness ofthe region in the second direction comprises changing the reflectivityof the region in the second direction with the second beam.